The present invention relates, in general, to a transmission system or an exchange used to exchange Synchronous Transfer Mode (hereinafter, referred to as "STM" for short, when applicable) signals and Asynchronous Transfer Mode (hereinafter, referred to as "ATM" for short, when applicable) signals, and more particularly to a method of processing inclusively the STM signals and the ATM signals, and a switching system employing the same.
Heretofore, as for such a technology, for example, as described in the paper of B. Pauwels et al.: "APPLICATION OF THE MULTIPATH SELF-ROUTING SWITCH IN A COMBINED STM/ATM CROSS-CONNECT SYSTEM", ISS 92, Oct. 1992, Vol. 1, C3.1, there is known a system wherein an STM signal is first of all packetized and then is processed in the similar manner to that in an ATM signal. A configuration of a switch according to that system is shown in FIG. 17. In the figure, the reference numerals 1-1 to 1-4 designate input highways, the reference numerals 4-1 to 4-4 designate output highways, and the reference numerals 35-1 to 35-4 and 36-1 to 36-4 designate transmission lines, respectively. As shown in FIG. 17, in this system, the STM signals which have been received by STM receiving interface units 30-1 and 30-2 are first of all packetized in respective packetizing units 41-1 and 41-2. During the packetizing operation, the information which is required for the switching operation is added as a header to the associated STM signal. In addition, in ATM receiving interface units 32-1 and 32-2 as well, the information required for the switching operation is added as a header to the associated ATM signal. A switching unit 40 operates to switch both the STM signals which have been packetized and the ATM signals, in accordance with the information which has been written to the respective headers. Thereafter, the STM signals are restored to their original signal forms in unpacketizing units 42-1 and 42-2, respectively, and then are output to the output highways via STM transmitting interface units 31-1 and 31-2, respectively. The ATM signals are output to ATM transmitting interface units 33-1 and 33-2, respectively, after the switching operation, and then are output to the output highways, respectively.
In this way, the STM signals are processed in a manner similar to that for processing the ATM signals, thereby realizing the inclusive switching of both the STM signals and the ATM signals.
In the above-mentioned prior art, the STM signals are temporarily stored to packetize them. Therefore, the time delay associated therewith increases necessarily. In addition, in the case where the STM signals are packetized to be exchanged, there is the possibility that the STM signals may be abandoned in the switching unit. In other words, in the case of exchange of the STM signals, it is necessary to secure the time slots in the highways on the input and output sides of the switching unit and to secure an area (addresses) for storing the STM signals in the data memory of the switching unit. However, in the above-mentioned prior art, those conditions can not be fulfilled.